staging: vchi: Get rid of struct vchiq_instance forward declaration

It's already forward declared in vchiq_if.h. So no need to insist

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20200629150945.10720-36-nsaenzjulienne@suse.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>